Water derived from ground water and surface supplies have always been "contaminated" with naturally occurring materials, such as hydrogen sulfide, iron, manganese, and certain naturally occurring heavy metals derived from the elemental content of the earth and from various biological reactions that occur. More recently these same contaminants, and many more, have been introduced into these sources of water by mining and industrial activities. For example, industrial waste solutions have introduced several heavy metal contaminants into potential sources for drinking water. Various effluents from nuclear processing plants have introduced, for example, uranium, radium, cobalt, barium, strontium and similar ions. Certain of these contaminants are also from naturally occurring sources. This increasing burden of contaminants, and a growing knowledge of the problems they produce, has gradually led to increases in the restrictions concerning the maximum levels of these contaminants at the "point of use" of the water. The Environmental Protection Agency has established the maximum acceptable concentration of these contaminants in drinking water, as listed in Table I.
Probably the most common media for the treatment of water to reduce various contaminants is an ion exchange resin. Depending upon the ions involved, this can be an anion resin, a cation resin or even a mixed resin medium. Generally, the resin beds are not selective as to the ions sorbed. The treatment process typically involves a regenerative bed where the sorbed ions are removed so as to condition the resin for additional removal. However, with some of the above-described contaminants, ion exchangers lack any appreciable affinity or lack the necessary selectivity to remove only the trace impurities.
TABLE I ______________________________________ EPA DRINKING WATER STANDARDS MAXIMUM LEVEL PARAMETER mg/l ______________________________________ Arsenic 0.05 Barium 1.0 Cadmium 0.01 Chromium 0.05 Copper 1.0 Iron 0.3 Lead 0.05 Manganese 0.05 Mercury 0.002 Selenium 0.01 Silver 0.05 Sulfide (Odor Threshold) 0.025 Radium 5 pCi/l 0.01 Gross Alpha 15 pCi/l Gross Beta 4 millirem/yr Turbidity 1/TU Coliform Bacteria 1/100 ml ______________________________________
There are certain organic and inorganic adsorbents that have been utilized in water treatment in the past. One such organic adsorbent is granulated activated carbon. While carbon has exceptional removal capabilities for chlorine and certain organic contaminants, carbon beds lack usefulness for most heavy metals and are usually used in combination with some other treatment method. Bacterial growth is also very prevalent within the carbon bed.
Various zeolites are known for their selective affinities for certain metal ions. For example, "Greensand" (Ionac M-50 available from Sybron Corp.) is a zeolite that has been treated with potassium permanganate to impregnate the surface with a layer of the higher oxidative oxides of manganese. This material has been used specifically for the oxidation and filtration of sulfide, iron and manganese. It has a limited capacity due to having only a surface coating of active material before "breakthrough" occurs, so must be frequently regenerated. When the media is "exhausted", it must be regenerated with more permanganate.
Two other materials having possible use in water treatment are KDF-55D (available from Orc, Inc.) and BIRM (available from Clack, Inc.). Both of these have very limited capacities and affinities and thus are not practical for the treatment of water sources with a variety of contaminants.
Research in this field has also been conducted in Japan, as reported in U.S. Pat. Nos. 4,551,254 and 4,581,219 issued to N. Imada on Nov. 5, 1985 and Apr. 8, 1986, respectively. In the work reported in these patents, powdered electrolytic manganese dioxide (EMD) of a certain type is immersed in an acidic solution of divalent manganese ions for several days. The mass that results is broken into pieces, classified to have a size of 20 to 48 mesh and neutralized. This results in a packing that has high surface activity and macroscopic pores through which water is able to pass readily. The initial powder has microscopic porosity and is of gamma form. After the processing the manganese dioxide is converted, according to the patent, into beta type (or a mixture of gamma and beta form). The macroporous nature of this product provides primarily filtration and not a catalytic or oxidation reaction to retain the contaminants. The product was studied for the removal of low levels of manganese, iron and primarily chromaticity (colored matter) from lakes or rivers. Contact times reported in these references are about 2.5 minutes.
In still other Japanese research, as reported in Japanese Laid Open Patent Application Number 63-194710 (laid open Aug. 11, 1988), alpha type manganese dioxide was tested and reported to be a better media for the removal of low levels (generally below the EPA limits) of contaminants from water than the media reported in the Imada patents.
All of this prior art dealing with electrolytic manganese dioxide teaches that there must be a conversion from the initial complete gamma form to another form (beta plus gamma, beta alone or alpha alone), and that the microscopic pore structure must be converted to a macroscopic pore media. The results obtained in this prior work do not show any breakthrough curves nor any capacities of the beds, and the tests are generally with very low levels of contamination of iron and manganese (from surface waters wherein these elements are in the oxidized state).
Thus, there is a teaching away from the use of an all gamma form electrolytic manganese dioxide where the microporous structure is retained for adsorption, ion exchange or oxidation-reduction purposes such that, as reported hereinbelow, reactions can occur to achieve high loadings, effective removal of elevated concentrations, significant throughput, and regeneration such that the media in a water purifier can be used over an extended time period. The subject media has the capability of removing sulfide, iron and manganese by oxidation, while removing heavy metals by adsorption. Further, this structure permits the removal of certain contaminating elements by a reduction mechanism (e.g., chlorine removal).
While manganese, iron and organic matter are common contaminants in many waters, the presence of heavy metals is an ever increasing problem and the removal thereof by conventional media has been found to be limited. The Japanese references do not even address the problems encountered in the removal of such contaminants.
Thus, the state-of-the-art of removing contaminants has demonstrated that a wide variety of media was required to selectively remove the various contaminants found to be present in the various sources of water including wells and surface water reservoirs. In order to achieve conformance with EPA standards, each source of water required an analysis and then a design of a purification system to best match removal of the contaminants present in that source. For some of the other contaminants, particularly the heavy metals, the known purification systems are silent as to the effectiveness of removal.
Accordingly, it is an object of the present invention to provide a process using a single inexpensive inorganic media that will selectively remove substantially all of the undesired contaminants found in typical water from wells and surface sources.
It is another object to provide a process using an inexpensive media for the removal of water contaminants where the media has sufficient capacity to minimize regeneration operations.
An additional object of the present invention is to provide a water treatment process using an inexpensive and effective media for the removal of contaminants where the media is readily regenerated when necessary.
A further object of the present invention is to provide an adsorbent media that can be used in large canisters for "point of entry" water treatment, or in smaller cartridges for "point of use" applications, such as in the home.
Another object of the present invention is to provide a process using a regenerable inorganic media capable of removing contaminants from well and surface water sources by catalytic oxidation or reduction, as well as heavy metal adsorption.
Yet another object is to provide a process for removing contaminants from water sources using a media which is itself bacteriastatic.
It is also an object of the present invention to provide a process that effectively, and inexpensively, removes heavy metals and similar constituents from water sources.
These and other objects of the present invention will become fully understood upon a consideration of the full description of the invention which follows.